Conventional piezoelectric acoustic transducers (“piezoelectric type loudspeaker”) use natural resonance of a diaphragm and a bending deformation of the diaphragm, which uses the converse piezoelectric effect, to reproduce sounds. This raises a problem that, as compared to electrodynamic loudspeakers having a diaphragm which has equivalent area, the conventional piezoelectric acoustic transducers have less bass reproduction capability. As means which overcomes such problem, there are piezoelectric type loudspeakers which have an edge and damper formed between a frame and a diaphragm (e.g., see Patent Literature 1).
FIG. 44 is an external view of a piezoelectric type loudspeaker disclosed in Patent Literature 1. A piezoelectric type loudspeaker 10 includes an outer frame 21, an inner frame 22, a piezoelectric element 30, diaphragms 41, 42, 43, and 44, dampers 51, 52, 53, 54, 55, 56, 57, and 58, and edges 61, 62, 63, and 64. In the piezoelectric type loudspeaker 10, application of an AC signal to the piezoelectric element 30 in a direction perpendicular to a main surface causes, because of the converse piezoelectric effect, the piezoelectric element 30 to expand or contract in a main surface direction, and therefore bending deformations occur with respect to the diaphragms 41 to 44. As a result, the piezoelectric type loudspeaker 10 generates a sound wave in the direction perpendicular to the main surface.
The piezoelectric type loudspeaker 10 having the above configuration is able to reduce stiffness of a support system by including the dampers 51 to 58 and the edges 61 to 64. Therefore, lowest resonant frequency can be reduced, and the limitation of the bass reproduction can be ameliorated as compared to the conventional piezoelectric type loudspeakers.